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United States Patent |
5,091,609
|
Sawada
,   et al.
|
February 25, 1992
|
Insulated wire
Abstract
An insulated electrical wire is suitable for use as a distribution wire, a
wire for winding coils, and for other electrical purposes. The wire can be
used in a high-vacuum environment or in a high-temperature environment.
This insulated electrical wire has a conductor core made of a base
material (1), an anodic oxide layer (2), and an oxide insulating layer
(3). The base material (1) forms a conductor core and has a surface cover
of either an aluminum layer or an aluminum alloy layer at least on its
outer surface. The anodic oxide layer (2) is formed on the surface layer.
The oxide insulating layer (3) is formed on the anodic oxide layer by a
sol-gel method or an organic acid salt pyrolytic method. This insulated
electrical wire has a good heat resistance and a good insulating strength
as well as excellent flexibility, and does not provide any gas adsorption
source.
Inventors:
|
Sawada; Kazuo (Osaka, JP);
Inazawa; Shinji (Osaka, JP);
Yamada; Kouichi (Osaka, JP)
|
Assignee:
|
Sumitomo Electric Industries, Ltd. (Osaka, JP)
|
Appl. No.:
|
598629 |
Filed:
|
October 12, 1990 |
PCT Filed:
|
February 13, 1990
|
PCT NO:
|
PCT/JP90/00177
|
371 Date:
|
October 12, 1990
|
102(e) Date:
|
October 12, 1990
|
PCT PUB.NO.:
|
WO90/09670 |
PCT PUB. Date:
|
August 23, 1990 |
Foreign Application Priority Data
| Feb 14, 1989[JP] | 1-34526 |
| Jan 31, 1990[JP] | 2-22854 |
Current U.S. Class: |
174/110A; 174/126.2; 427/123; 427/126.4; 428/384 |
Intern'l Class: |
H01B 007/02; H01B 003/10 |
Field of Search: |
174/110 A,126.2
428/375,378,384,388
427/123,126.2,126.3,126.4
|
References Cited
U.S. Patent Documents
2088949 | Aug., 1937 | Fekete | 174/110.
|
3961111 | Jun., 1976 | Smith, deceased | 427/419.
|
4288299 | Sep., 1981 | Carter | 204/38.
|
4417097 | Nov., 1983 | Das | 174/110.
|
4483751 | Nov., 1984 | Murayama et al. | 204/37.
|
4620086 | Oct., 1986 | Ades et al. | 174/110.
|
4738896 | Apr., 1988 | Stevens | 428/378.
|
Foreign Patent Documents |
188369 | Jul., 1986 | EP.
| |
188370 | Jul., 1986 | EP.
| |
51-93976 | Jul., 1976 | JP.
| |
56-149775 | Nov., 1981 | JP.
| |
165909 | Jul., 1986 | JP.
| |
165910 | Jul., 1986 | JP.
| |
63-239150 | Oct., 1988 | JP.
| |
63-247374 | Oct., 1988 | JP.
| |
63-279524 | Nov., 1988 | JP.
| |
Primary Examiner: Nimmo; Morris H.
Attorney, Agent or Firm: Fasse; W. G., Kane, Jr.; D. H.
Claims
We claim:
1. An insulated electrical wire having a conductor core surrounded by
insulation comprising: a conductor core, a surface layer at least on the
outer surface of said conductor core, said surface layer being made of a
member selected from the group consisting of aluminum and aluminum alloys,
an anodic oxide layer (2) on said surface layer, said anodic oxide layer
having holes and pores therein, and an oxide insulating layer (3) bonded
to said anodic oxide layer, said oxide insulating layer filling said holes
and pores of said anodic oxide layer, said oxide insulating layer and said
anodic oxide layer forming together a composite insulating coating on said
outer surface of said conductor core, said composite insulating coating
having an outer smooth surface.
2. The insulated electrical wire of claim 1, wherein said conductor core is
made of a material selected from the group consisting of copper and copper
alloys.
3. The insulated electrical wire of claim 2, wherein said surface layer on
said conductor core is prepared by a pipe cladding method.
4. The insulated electrical wire of claim 1, wherein said oxide insulating
layer is made of at least one member selected from the group consisting of
silicon oxide and aluminum oxide.
5. The insulated electrical wire of claim 1, wherein said oxide insulating
layer is formed on said anodic oxide layer by a sol-gel method.
6. The insulated electrical wire of claim 1, wherein said oxide insulating
layer is formed on said anodic oxide layer by an organic acid salt
pyrolytic method.
7. The insulated electrical wire of claim 6, wherein said conductor core is
made of a material selected from the group consisting of copper and copper
alloys.
8. The insulated electrical wire of claim 7, wherein said surface layer on
said conductor core is prepared by a pipe cladding method.
9. The insulated electrical wire of claim 6, wherein said oxide insulating
layer is made of at least one member selected from the group consisting of
silicon oxide and aluminum oxide.
10. The insulated electrical wire of claim 1, wherein said oxide insulating
layer is formed by applying a solution containing a ceramics precursor,
onto said anodic oxide layer and thereafter completely bringing said
ceramics precursor to a ceramic state.
Description
FIELD OF THE INVENTION
The present invention relates to an insulated electrical wire, and more
particularly, it relates to an insulated wire such as a distribution wire,
a wire for winding coils or the like which is employed in a
high-vacuum-environment or in a high-temperature environment as may
prevail in a high-vacuum apparatus or in a high-temperature service
apparatus.
BACKGROUND INFORMATION
An insulated electrical wire may be used in equipment such as heating
equipment or in a fire alarm device for which safety under a high
temperature is required. Further, an insulated wire of this type is also
used in the environment of an automobile, which is heated to a high
temperature by the engine. An insulated wire formed by an electrical
conductor which is coated with heat resistant organic resin such as
polyimide, fluorocarbon resin or the like has generally been used for the
above purposes.
Mere organic coatings are insufficient for applications requiring a high
heat resistance or for use in a environment for which a high degree of
vacuum is required, because an organic coating has an insufficient heat
resistance, and due to a gas emission property and the like. Thus, an
insulated wire having a conductor inserted in an insulator tube of
ceramics, or an MI cable (Mineral Insulated Cable) having a conductor
inserted in a heat resistant alloy tube of a stainless steel alloy etc.
which is filled with metal oxide powder of magnesium oxide etc., or the
like has been used in high temperature and vacuum environments.
A fiber-glass braided insulated wire employing textile glass fiber as an
insulating member etc. is listed as an insulated wire satisfying
flexibility and heat resistance requirements.
In the aforementioned insulated wire coated with a heat-resistant organic
resin, the highest temperature at which an adequate electric insulation
can be maintained, is about 200.degree. C. at the most. Therefore, it has
been impossible to use such an organic insulation coated wire under
conditions requiring a guarantee of an adequate electrical insulation at a
high temperature of at least 200.degree. C.
Further, the insulated wire which is improved in its heat resistance by an
insulator tube of ceramics, has disadvantages such as an inferior
flexibility. The MI cable comprising a heat resistant alloy tube
surrounding a conductor, has an increased outer diameter with respect to
the conductor radius. Thus, the MI cable has a relatively large
cross-section with respect to electric energy that can be carried by the
conductor passing through the heat resistant alloy tube. In order to use
the MI cable as a wire for winding a coil in a bobbin or the like,
however, it is necessary to bend the heat resistant alloy tube in a
prescribed curvature which is difficult. For example, it is difficult to
obtain a suitable winding density since the tube forming the outer
enclosure is thick compared to the conductor.
Further, when the fiber-glass braided, heated resistant, insulated wire is
employed and worked into a prescribed configuration as required for its
application, the network of the braid is disturbed resulting in a
breakdown. In addition, dust of glass is generated by the glass fibers.
This glass dust may serve as a gas adsorption source. Therefore, when the
fiber-glass braided insulated wire is used in an environment for which a
high degree of vacuum is required, it has been impossible to maintain a
high degree of vacuum due to the gas adsorption source by the glass dust.
SUMMARY OF THE INVENTION
Accordingly, the present invention has been proposed in order to solve the
aforementioned problems, and its object is to provide an insulated
electrical conductor wire comprising the following features:
(a) It has a high electrical insulating strength under a high temperature
operating conditions,
(b) it has an excellent flexibility, and
(c) it does not comprise any gas adsorption source.
An insulated wire according to one aspect of the present invention
comprises a base material, an anodic oxide film, or said base material and
an oxide insulating layer or said anodic oxide film. The base material
includes an electrical conductor, and has a surface layer of either an
aluminum layer or an aluminum alloy layer at least on its outer surface.
The oxide insulating layer is formed on the anodic oxide layer by a
sol-gel method.
When the base material is worked into a composite conductor, a material
containing either copper or a copper alloy is used by way of example, for
the core of the base material. In this case, the base material is
preferably prepared by a pipe cladding method. The oxide insulating layer
preferably contains at least either silicon oxide or aluminum oxide.
An insulated wire according to another aspect of the present invention
comprises a base material, an anodic oxide layer, on the base material and
an oxide insulating layer on the oxide layer. The base material includes a
conductor, and has a surface layer of either an aluminum layer or an
aluminum alloy layer at least on its outer surface. The oxide insulating
layer is formed on the anodic oxide layer by an organic acid salt
pyrolytic method.
The core of the base material may contain either copper or a copper alloy.
In this case, the base material is preferably prepared by a pipe cladding
method. The organic insulating layer preferably contains at least either
silicon oxide or aluminum oxide.
The oxide insulating layer of the present invention is formed by applying a
solution containing a ceramics precursor, onto the anodic oxide layer and
thereafter completely bringing the ceramics precursor into a ceramics
state. The solution containing the ceramics precursor is a solution of a
metal organic compound of high polymers having an alkoxide group, a
hydroxy group and metalloxan bonding, which is generated by hydrolysis and
a dehydration/condensation reaction of a compound having a hydrolyzable
organic group such as a metal alkoxide, and contains an organic solvent
such as alcohol, the metal alkoxide of the raw material, a small amount of
water, and a catalyst which are required for the hydrolysis. In another
embodiment the oxide insulation layer is formed of a solution which is
obtained by mixing or dissolving metal organic compounds in a proper
organic solvent. Further, the metal organic compounds mentioned herein
exclude those in which elements directly bonded to the metal atoms are all
carbon. Stated differently, the metal organic compounds employed in the
present invention are restricted to those having thermal decomposition
temperatures lower than the boiling points of the metal organic compounds
under atmospheric pressure, since the present metal oxide film is obtained
by thermally decomposing the metal organic compounds by heating.
The above mentioned sol-gel method for the formation of the insulation
oxide film, is a solution method, wherein a solution prepared by
hydrolyzing and dehydrating or condensing metal alkoxide is applied onto
an outer surface to be coated such as a base material and thereafter
treating the coated material at a prescribed temperature, thereby forming
the oxide insulating layer. The film or layer formed by the sol-gel method
is an oxide which is brought into a ceramics state. This oxide is
preferably formed by a heat treatment in an atmosphere of an oxygen gas
current. The oxide insulating layer thus brought into a ceramics state
exhibits excellent heat resistance and insulating strength under high
temperature operating conditions of at least 500.degree. C.
In another aspect of the present invention, an anodic oxide film is formed
on an aluminum layer or an aluminum alloy layer, and an insulating oxide
film is formed on the anodic oxide film by an organic acid salt pyrolytic
method, which is a solution method. The organic acid salt pyrolytic
methods forms a metal oxide by pyrolyzing an organic acid salt, i.e.,
metallic salt such as naphthenic acid, capric acid, stearic acid, octylic
acid or the like. A film formed by the organic acid salt pyrolytic method
is an oxide which is brought into a ceramics state. This oxide is
preferably formed by a heat treatment in an atmosphere of an oxygen gas
current. The oxide insulating layer thus brought into a ceramics state
exhibits an excellent heat resistance and insulability strength under a
high temperature of at least 500.degree. C.
The anodic oxide film strongly adheres to the aluminum layer or the
aluminum alloy layer. Further, this anodic oxide film also functions to
some extent as an insulator. However, the anodic oxide film has a rough
surface. Therefore, the outer surface of the anodic oxide film has a large
surface area, and provides a gas adsorption source. Therefore, a conductor
which is formed with only an anodic oxide film on its outer surface cannot
be used in a high vacuum environment.
Further, the anodic oxide film is porous and has a large number of holes
passing from its surface toward the base material. Thus, it is generally
impossible to obtain an insulating strength which is proportional to the
film thickness of the anodic oxide film.
To this end, the inventors have found that it is possible to form a film or
layer for filling up the holes of the anodic oxide film and simultaneously
covering the irregular surface thereby smoothing the surface, by forming
an oxide film on the outer surface of the anodic oxide film through the
sol-gel method or the organic acid salt pyrolytic method. Thus, it is
possible to obtain a high breakdown voltage characteristics which is
proportional to the film thickness, as well as to reduce the gas
adsorption source by decreasing the outer surface area.
Further, the anodic oxide film adheres excellently to the aluminum layer or
the aluminum alloy layer forming at least the outer surface of the base
material. Thus, the adhesion between the oxide film and the outer surface
of the base material is improved as compared with the case of directly
forming an oxide film on the outer surface of a conductor by the sol-gel
method or the organic acid salt pyrolytic method. Therefore, the insulated
wire according to the present invention has a good heat resistance, a good
flexibility, and a good insulating strength under high temperature
operating conditions.
BRIEF DESCRIPTION OF THE DRAWINGS
FIGS. 1 and 2 are sectional views showing cross sections of insulated wires
according to the present invention corresponding to respective Examples 1
and 3 as well as 2 and 4.
DETAILED DESCRIPTION OF PREFERRED EXAMPLE EMBODIMENTS AND OF THE MODES OF
CARRYING OUT THE INVENTION
Example 1
(a) Formation of an Anodic Oxide Film
A pure aluminum wire having a diameter of 2 mm.phi. was dipped in diluted
sulfuric acid of 23 percent by weight, which was maintained at a
temperature of 38.degree. C. Thereafter a positive voltage was applied to
the aluminum wire, and the outer surface of the pure aluminum wire was
anodized with a bath current of 2.5 A/dm.sup.2 maintained for 20 minutes.
Thus, an anodic oxide film was formed on the outer surface of the pure
aluminum wire with a film thickness of about 20 .mu.m. The as obtained
wire was dried in an oxygen gas current at a temperature of 500.degree. C.
(b) Preparation of a Coating Solution Used in the Sol-Gel Method
1.2 N of concentrated nitric acid was added to a solution, which was
prepared by mixing tetrabutylorthosilicate, water, and ethanol in mole
ratios 8:32:60, in the ratio of 1/100 mole of tetrabutylorthosilicate.
Thereafter this solution was heated and stirred at a temperature of
70.degree. C. for two hours.
(c) Coating
The wire obtained by (a) was dipped in the coating solution of (b). A
heating step was performed at a temperature of 400.degree. C. for 10
minutes and five times on the wire outer surface of which had been coated
with the coating solution. IN an initial stage of this step, a
characteristic rough surface, which was formed by the anodic oxidation
treatment, disappeared due to the heat treated surface which was observed
with an electron microscope. The heat treatment resulted in a structure
wherein the rough portions were impregnated with oxides. It has been
confirmed that a film was formed on the exterior of the impregnated layer
by repeating the heating step. Finally, this wire was heated in an oxygen
gas current at a temperature of 500.degree. C. for 10 minutes.
An insulated coated wire obtained in the aforementioned manner is shown in
FIG. 1 showing a cross sectional view of the insulated wire according to
the present invention. Referring to FIG. 1, an anodic oxide film 2 is
formed on the outer surface of an aluminum wire 1. An oxide insulating
layer 3 is formed on this anodic oxide film 2 by the sol-gel method. In
the aforementioned Example 1, this oxide insulating layer 3 is made of
silicon oxide. In Example 1, the coating thickness of the insulating
coating formed by the anodic oxide film 2 and by the oxide insulating
layer 3 was about 40 .mu.m.
The breakdown voltage was measured in order to evaluate the insulating
strength of the insulated wire of Example 1. Its breakdown voltage was 1.6
kV at room temperature, and was 1.2 kV at a temperature of 600.degree. C.
When this insulated wire was wound onto the outer peripheral surface of a
cylinder having a diameter of 5 cm, no cracking of the insulating layer
occurred.
Example 2
(a) Formation of an Anodic Oxide Film
An aluminum clad copper wire having a conductivity of 84% IACS on the
assumption that the conductivity of pure copper is 100, and a diameter of
1 mm.phi. was used in this Example 2. Such a wire has a core of oxygen
free copper (OFC) enclosed by an outer layer of aluminum (JIS nominal
1050) having a layer thickness of 100 .mu.m. This aluminum clad copper
wire was dipped in diluted sulfuric acid of 23 percent by weight which was
maintained at a temperature of 30.degree. C. Thereafter a positive voltage
was applied to the aluminum clad copper clad wire, to anodize the outer
surface of the aluminum layer with of a bath current of 15 A/dm.sup.2
maintained for two minutes. Thus, an anodic oxide film was formed on the
surface of the aluminum clad copper wire. The anodic film had a thickness
of about 10 .mu.m. The as-formed wire was dried in an oxygen gas current
at a temperature of 500.degree. C.
(b) Preparation of a Coating Solution Used in the Sol-Gel Method
Tributoxyaluminum, triethanolamine, water and ethanol were mixed in mole
ratios 3:7:9:81 at a temperature of about 5.degree. C. Thereafter this
solution was heated and stirred at a temperature of 30.degree. C. for one
hour.
(c) Coating
The coating treatment of the wire was performed similar to Example 1.
An insulated coated wire obtained in the aforementioned manner is shown in
FIG. 2, showing a cross-sectional view. Referring to FIG. 2, an aluminum
clad copper clad wire having an aluminum layer 11 on the outer surface of
a copper core 10 was employed as a base material. An anodic oxide film 2
is formed on the outer surface of this aluminum layer 11. An oxide
insulating layer 3 is formed on the anodic oxide film 2 by the sol-gel
method. In the aforementioned Example 2, this oxide insulating layer 3 is
of aluminum oxide. According to the aforementioned Example 2, further, the
coating thickness of an insulating coating formed by the anodic oxide film
2 and by the oxide insulating layer 3 was about 20 .mu.m.
The breakdown voltage was measured in order to evaluate the insulating
strength of the insulated wire. Its breakdown voltage was 1.5 kV at room
temperature, and was 1.0 kV at a temperature of 500.degree. C. When this
insulated wire was wound onto the outer peripheral surface of a cylinder
having a diameter of 3 cm, no cracks occurred in the insulating layer.
Example 3
(a) Formation of the Anodic Oxide Film
A pure aluminum wire having a wire diameter of 1 mm was dipped in diluted
sulfuric acid of 23 percent by weight, which was maintained at a
temperature of 35.degree. C. Thereafter a positive voltage was applied to
the aluminum wire, to anodize the outer surface of the pure aluminum wire
with a bath current of 5 A/dm.sup.2 maintained three minutes. Thus, an
anodic oxide film was formed on the outer surface of the pure aluminum
wire with a film thickness of about 17 .mu.m. The as-formed wire was dried
in an oxygen gas current at a temperature of 400.degree. C.
(b) Preparation of the coating solution Used in the Organic Acid Salt
Pyrolytic Method
Silicate stearate was dissolved in a mixed solution of 90 ml of toluene, 10
ml of pyridine and 6 ml of propionic acid. The concentration of this
solution was so adjusted that the metal concentration of silicon was 5
percent by weight.
(c) Coating
The wire obtained as described under (a) of Example 3 was dipped in the
coating solution prepared as described under (b) of Example 3. Heating
steps at a temperature of 400.degree. C. were performed ten times for 10
minutes each on the wire the outer surface of which was thus coated with
the coating solution. Finally this wire was heated in an oxygen gas
current at a temperature of 450.degree. C. for 10 minutes.
An insulated coated sire obtained in the aforementioned manner is shown in
FIG. 1. FIG. 1 is a sectional view of the insulated wire according to the
present invention. Referring to FIG. 1, an anodic oxide film 2 is formed
on the outer surface of an aluminum wire 1. An oxide insulating layer 3 is
formed on this anodic oxide film 2 by an organic acid salt pyrolytic
method. In the aforementioned Example 1, this oxide insulating layer 3 is
of silicon oxide. According to the aforementioned Example 1, further, the
coating thickness of an insulating coating formed by the anodic oxide film
2 and by the oxide insulating layer 3 was about 25 .mu.m.
The breakdown voltage was measured in order to evaluate the insulating
strength of the obtained insulated wire. Its breakdown voltage was 1.2 kV
at room temperature, and was 0.8 kV at a temperature of 600.degree. C.
When this insulated wire was wound onto the outer peripheral surface of a
cylinder having a diameter of 3 cm, the insulating layer did not crack.
Example 4
(a) Formation of Anodic Oxide Film
An aluminum clad copper wire having a conductivity of 89% IACS on the
assumption that the conductivity of pure copper is 100, and a diameter of
1 mm.phi. was used in this Example 4. Such a wire has a core of oxygen
free copper (OFC) enclosed by an outer layer of aluminum (JIS nominal
1050) having a layer thickness of 83 .mu.m. This aluminum clad copper wire
was dipped in diluted sulfuric acid of 23 percent by weight, which was
maintained at a temperature of 35.degree. C. Thereafter a positive voltage
was applied to the aluminum clad copper wire, to anodize the outer surface
of the aluminum layer under a condition of a bath current of 3.5
A/dm.sup.2 maintained for two minutes. Thus, an anodic oxide film was
formed on the surface of the aluminum clad copper wire. The anodic oxide
film had a thickness of about 15 .mu.m. The so-formed wire was dried in an
oxygen gas current at a temperature of 300.degree. C.
(b) Preparation of the Coating Solution Used in the Organic Acid Salt
Pyrolytic Method
An O-cresol solution of aluminum octanate was prepared having a
concentration so adjusted that the metal concentration of aluminum was 4
percent by weight.
(c) Coating
A coating treatment of the wire was performed similar to Example 3.
An insulated coated wire obtained in the aforementioned manner is shown in
FIG. 2. FIG. 2 showing a cross sectional view. Referring to FIG. 2, an
aluminum clad copper clad wire having an aluminum layer 11 on the outer
surface of a copper core 10 was employed as a base material. An anodic
oxide film 2 is formed on the outer surface of this aluminum layer 11. An
oxide insulating layer 3 is formed on this anodic oxide film 2 by the
organic acid salt pyrolytic method. So in the aforementioned Example 2,
the oxide insulating layer 3 of Example 4 is also of aluminum oxide.
According to the aforementioned Example 4, the coating thickness of an
insulating coating formed by the anodic oxide film 2 and by the oxide
insulating layer 3 was about 30 .mu.m.
The breakdown voltage was measured in order to evaluate the insulation
strength of the so-formed insulated wire. Its breakdown voltage was 1.6 kV
at the room temperature, and was 1.2 kV at a temperature of 400.degree. C.
Also when this insulated wire was wound onto the outer peripheral surface
of a cylinder having a diameter of 3 cm, the insulating layer did not
crack.
Industrial Availability
As hereinabove described, the insulated wire according to the present
invention is suitable for a distribution wire, a wire for winding etc.
which is employed in a high-vacuum environment, or in a high-temperature
environment such as a high-vacuum apparatus, or in a high-temperature
service apparatus.
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